Catalyst apparatus for internal combustion engine

ABSTRACT

A catalyst apparatus is disposed in an exhaust passage for exhaust gas discharged from an internal combustion engine and includes a catalyst section for purifying the exhaust gas, and a heater section disposed upstream of the catalyst section in the exhaust passage and adapted to heat the exhaust gas. The pressure loss of the catalyst section in the flow velocity direction of the exhaust passage is smaller than the pressure loss of the catalyst section in a direction orthogonal to the flow velocity direction, and the heat capacity of the catalyst section is larger than the heat capacity of the heater section.

This application claims the benefit of Japanese Patent Applications No. JP 2017-070680 filed Mar. 31, 2017 and No. 2018-031571, filed Feb. 26, 2018, which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a catalyst apparatus for an internal combustion engine.

BACKGROUND OF THE INVENTION

A conventionally known catalytic converter is disposed in an exhaust passage of an internal combustion engine and adapted to clean HC, CO, NOx, etc. in exhaust gas (see Japanese Unexamined Publication No. H05-184938). This catalytic converter is configured to cause only a central portion of a honeycomb catalytic carrier formed of metal to generate heat, and the heat capacity of the central portion is smaller than that of an outer circumferential side thereof. Thus, upon energization, the central portion generate heat quickly, whereby exhaust gas at low temperature can be heated in an early stage, and catalytic reaction can be promoted.

Problem to be Solved by the Invention

Incidentally, the honeycomb carrier is configured such that the pressure loss in the flow velocity direction (axial direction) of the exhaust passage is smaller than that in the radial direction. As will be described later, the actual evidence provided by the present inventors reveals that heat conduction in the radial direction is considerably low. Namely, when the central portion of the catalytic carrier is heated as in the technique described in Japanese Unexamined Publication No. H05-184938, the heat is not transferred sufficiently to the outer circumferential side thereof. Therefore, activation of a catalyst at low temperature is difficult.

Thus, an object of the present invention is to provide a catalyst apparatus for an internal combustion engine which can activate a catalyst in an early stage when the temperature of exhaust gas is low.

SUMMARY OF THE INVENTION Means for Solving the Problem

In order to solve the above problem, a catalyst apparatus for an internal combustion engine of the present invention is a catalyst apparatus which is disposed in an exhaust passage for exhaust gas discharged from an internal combustion engine, comprising a catalyst section that is configured to purify the exhaust gas and a heater section disposed upstream of the catalyst section in the exhaust passage and adapted to heat the exhaust gas, wherein a pressure loss of the catalyst section in a flow velocity direction of the exhaust passage is smaller than a pressure loss of the catalyst section in a direction orthogonal to the flow velocity direction, and a heat capacity of the catalyst section is larger than a heat capacity of the heater section.

According to the present catalyst apparatus for the internal combustion engine, the heat capacity of the catalyst section is larger than the heat capacity of the heater section. Therefore, the heater section can generate heat quickly so as to heat exhaust gas at low temperature more early, thereby reliably promoting a catalytic reaction at the catalyst section.

Since the pressure loss of the catalyst section in the flow velocity direction of the exhaust passage is smaller than the pressure loss of the catalyst section in the direction orthogonal to the flow velocity direction, heat is not transferred sufficiently in the radial direction of the catalyst section. In view of this, the heater section is disposed on the upstream side of the catalyst section. In this case, since exhaust gas heated by the heater section flows through the entire catalyst section within the exhaust passage, it is possible to reliably heat the catalyst section, to thereby promote the catalytic reaction.

Also, since the heat capacity of the catalyst section is large, the catalyst section having become warm as a result of heat generation by the heater section cools slowly even after interruption of the energization of the heater section. Thus, the time during which the energization of the heater section is interrupted can be extended accordingly, whereby electric power can be saved.

The catalyst apparatus for the internal combustion engine of the present invention may further comprises a control section which is configured to use regenerated energy of a vehicle including the internal combustion engine as electric power for energizing the heater section.

According to the present catalyst apparatus for the internal combustion engine, regenerated energy is utilized for energization of the heater section, whereby electric power is saved.

In the catalyst apparatus for the internal combustion engine of the present invention, the heater section and the catalyst section may be adjacently disposed in a common casing.

According to the present catalyst apparatus for the internal combustion engine, it is possible to dispose the heater section and the catalyst section in a common casing while saving the space for installation and decreasing heat loss.

The catalyst apparatus for the internal combustion engine of the present invention may further comprise a retainer that is disposed to contact an upstream side of the heater section. In the catalyst apparatus, the heater section may be in contact with the catalyst section, the retainer has an insulating property and allows passage of the exhaust gas therethrough, and the heater section may be sandwiched between the retainer and the catalyst section.

According to the present catalyst apparatus for the internal combustion engine, these members can be reliably fixed within the exhaust passage.

In the catalyst apparatus for the internal combustion engine of the present invention, the catalyst section may include at least a reduction catalyst.

The reduction catalyst is small in amount of heat generation as compared with an oxidation catalyst. Therefore, the present invention is particularly effective. Examples of the reduction catalyst include an SCR (reduction), a three-way catalyst (reduction/oxidation), and ab NOx storage and reduction catalyst (storage/reduction).

Effect of the Invention

According to the present invention, a catalyst apparatus for an internal combustion engine which can activate a catalyst in an early stage when the temperature of exhaust gas is low can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein like designations denote like elements in the various views, and wherein:

FIG. 1 is a schematic view showing the configuration of a catalyst apparatus for an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is schematic view showing the structure of a catalyst section.

FIG. 3 is a plan view showing the structure of a heater section.

FIG. 4 is a perspective view showing the structure of a metal thin plate of the heater section.

FIG. 5 is a schematic view showing a state in which the heater section is sandwiched between a retainer and the catalyst section.

FIG. 6 is schematic view showing a measurement portion of the heater section used for measurement of heat capacity.

FIG. 7 is a view showing conditions under which the temperature distribution of a catalyst section having a reduced pressure loss in a flow velocity direction is simulated.

FIG. 8 is an illustration showing results of the simulation of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will next be described with reference to the drawings.

FIG. 1 is a schematic view showing the configuration of a catalyst apparatus 10 for an internal combustion engine according to an embodiment of the present invention, FIG. 2 is a schematic view showing the structure of a catalyst section 6, FIG. 3 is a plan view showing the structure of a heater section 4, and FIG. 5 is a schematic view showing a state in which the heater section 4 is sandwiched between a retainer 2 and the catalyst section 6.

As shown in FIG. 1, a vehicle 100 is a diesel vehicle including an internal combustion engine (e.g., a diesel engine) 102 and a motor 104. The internal combustion engine 102 and the motor 104 drive tires 106.

The catalyst apparatus 10 is disposed in an exhaust passage 108 for exhaust gas discharged from the internal combustion engine 102. The catalyst apparatus 10 has a canning structure in which the catalyst section 6, the heater section 4 disposed upstream of the catalyst section 6, and the retainer 2 disposed upstream of the heater section 4 are press-fitted in a casing 8. The catalyst apparatus 10 has a control section 9 (microcomputer) for controlling energization of the heater section 4, and the control section 9 is connected to a vehicle-side ECU 110.

The catalyst section 6 purifies exhaust gas and has an SCR catalyst shown in FIG. 2 in the present embodiment. The SCR catalyst 6 a is formed of a cylindrical ceramic porous member having a large number of holes 6 h extending in a flow velocity direction (axial direction) F. A catalyst such as vanadium is carried by this ceramic carrier. Also, the catalyst section 6 also has a urea water injector 6 b and a DPF (Diesel Particulate Filter) 6 c disposed upstream of the SCR catalyst 6 a as shown in FIG. 5.

The pressure loss of the SCR catalyst 6 a in the flow velocity direction F is smaller than the pressure loss in the radial direction, which is the direction orthogonal to the flow velocity direction F. Thus, a catalytic reaction occurs in a state in which the exhaust gas smoothly flows in the exhaust passage 108 while passing through the holes 6 h.

As shown in FIG. 3, the heater section 4 has a honeycomb structure in which a single metal thin plate 4 a having an insulation sheet 4 b stacked on one side thereof is wound spirally. A positive electrode 4 d and a negative electrode 4 e are connected to the center side and the outer circumferential side of the metal thin plate 4 a. When electricity is supplied to lead wires 4L1 and 4L2 connected to the two electrodes 4 d and 4 e, the metal thin plate 4 a generates heat.

Also, as shown in FIG. 4, the metal thin plate 4 a is corrugated along the longitudinal direction such that as a result of winding, a large number of gaps extending along the flow velocity direction (axial direction) F are formed, thereby securing passage of gas.

Thus, the heater section 4 heats the exhaust gas, whereby the exhaust gas at low temperature is heated in an early stage, and the catalytic reaction at the catalyst section 6 on the downstream side is promoted.

Notably, the metal thin plate 4 a can be formed of, for example, Fe—Cr—Al alloy, and the insulation sheet 4 b can be formed of, for example, fabric woven from alumina wire.

Further, as shown in FIG. 5, the retainer 2 is a cylindrical ceramic porous member having a center opening 2 c and a large number of holes 2 h extending along the flow velocity direction (axial direction) F. The lead wires 4L1 and 4L2 of the heater section 4 extend outward from the center opening 2 c of the retainer 2.

The heater section 4 is axially retained between the retainer 2 and the catalyst section 6, whereby these members are fixed within the casing 8.

The control section 9 performs such control as to use energy (electric power) regenerated by the motor 104 in the course of deceleration of the vehicle 100 as power for energizing the heater section 4 for heating. This control can be performed, for example, by connecting, by means of switching, the lead wires 4L1 and 4L2 of the heater section 4 to a battery which is charged with the regenerated energy (electric power).

Also, the control section 9 shuts off electricity supplied to the heater section 4 for saving electricity if energization is unnecessary (e.g., when exhaust gas is sufficiently warm).

In the present embodiment, the heat capacity of the catalyst section 6 is larger than the heat capacity of the heater section 4. Therefore, the heater section 4 can generate heat quickly so as to heat exhaust gas at low temperature more early, thereby reliably promoting the catalytic reaction at the catalyst section 6.

Since the pressure loss of the catalyst section 6 in the flow velocity direction F of the exhaust passage 108 is smaller than the pressure loss of the catalyst section 6 in the direction orthogonal to the flow velocity direction F, if the heater section 4 is disposed at the center of the catalyst section 6, heat is not transferred sufficiently in the radial direction of the catalyst section 6. In view of this, the heater section 4 is disposed on the upstream side of the catalyst section 6. In this case, since exhaust gas heated by the heater section 4 flows through the entire catalyst section 6 within the exhaust passage 108, it is possible to reliably heat the catalyst section 6, to thereby promote the catalytic reaction.

Also, since the heat capacity of the catalyst section 6 is large, the catalyst section 6 having become warm as a result of heat generation by the heater section 4 cools slowly even after interruption of the energization of the heater section 4. Thus, the time during which the energization of the heater section 4 is interrupted can be extended accordingly, whereby electric power can be saved.

FIGS. 7 and 8 show the results of a simulation for determining a temperature distribution in a catalyst section (porous member) having a reduced pressure loss in the flow velocity direction and temperature distributions on upstream and downstream sides of the catalyst section (porous member) in the gas flow velocity direction.

As shown in FIG. 7, the simulation was performed under the conditions that an upstream space and a downstream space are present on the upstream and downstream sides, respectively, of the catalyst section (porous member) in the gas flow velocity direction. Notably, the catalyst section (porous member) is configured such that a heat generation section is present at a center portion and a non-heat generation section is present on the outer circumferential side thereof.

FIG. 8 shows the temperature distributions; i.e., the results of the simulation. As shown in FIG. 8, the space on the downstream side of the catalyst section (porous member); specifically, the space on the downstream side of the center portion where the heat generation section is present, is high in temperature (a gray region of FIG. 8). Of the catalyst section (porous member), the heat generation section (center portion) has a high temperature (a white region of FIG. 8), and a portion on the outer circumferential side of the heat generation section has a low temperature approximately the same as the temperature before introduction of gas (a black region of FIG. 8). As described above, in the catalyst section having a reduced pressure loss in the flow velocity direction, even when the heat generation section (center portion) generates heat, the heat is not transferred sufficiently to the outer circumferential side. It was found from this that the heat conduction in the radial direction is considerably low.

Notably, this simulation was performed on the assumption that the flow of the gas is a uniform flow along the exhaust passage. However, even in the case where the gas does not flow along the exhaust passage and its flow has components in different directions, it is presumed that similar temperature distributions are obtained, because the pressure loss of the catalyst section in the flow velocity direction (axial direction) of the exhaust passage is smaller than the pressure loss in the radial direction.

The heat capacities of the catalyst section 6 and the heater section 4 are obtained as follows. The catalyst section 6 and the heater section 4 are individually placed in a thermostatic chamber filled with the atmosphere of 300° C. The temperatures of the catalyst section 6 and the heater section 4 are monitored, and their time constants are obtained from changes in their temperatures with time. The heat capacities of the catalyst section 6 and the heater section 4 are calculated from the time constants.

Also, as shown in FIG. 6, in the case of a heater section 40 which is composed of a portion located in the interior 108 i of the exhaust passage 108, a portion screwed to the side wall of the exhaust passage 108, and a portion located outside the exhaust passage 108, only the portion 40 i located in the interior 108 i of the exhaust passage 108 is cut and taken out, and is used for measurement of the heat capacity.

The same also applies to the catalyst section 6.

The present invention is not limited to the above embodiment, but extends into various modifications and equivalents encompassed by the ideas and scope of the invention. For example, no particular limitation is imposed on the structures and shapes of the retainer, the heater section, and the catalyst section. Also, the material of the catalyst section 6 is not limited to the ceramic porous member so long as the pressure loss in the flow velocity direction is smaller than the pressure loss in the direction orthogonal to the flow velocity direction. For example, the catalyst section 6 may be formed by winding a metal thin plate 4 a coated with an insulating film which is formed of alumina or the like and which carries thereon a catalytic metal or the like.

DESCRIPTION OF REFERENCE NUMERALS

-   -   2: retainer     -   4: heater section     -   6: catalyst section     -   8: casing     -   9: control section     -   10: catalyst apparatus for internal combustion engine     -   100: internal combustion engine     -   108: exhaust passage 

1. A catalyst apparatus for an internal combustion engine which is disposed in an exhaust passage for exhaust gas discharged from an internal combustion engine, comprising: a catalyst section that is configured to purify the exhaust gas; and a heater section disposed upstream of the catalyst section and adapted to heat the exhaust gas, wherein a pressure loss of the catalyst section in a flow velocity direction of the exhaust passage is smaller than a pressure loss of the catalyst section in a direction orthogonal to the flow velocity direction, and a heat capacity of the catalyst section is larger than a heat capacity of the heater section.
 2. The catalyst apparatus for the internal combustion engine according to claim 1, further comprising a control section which is configured to use regenerated energy of a vehicle including the internal combustion engine as electric power for energizing the heater section.
 3. The catalyst apparatus for the internal combustion engine according to claim 1, wherein the heater section and the catalyst section are adjacently disposed in a common casing.
 4. The catalyst apparatus for the internal combustion engine according to claim 1, further comprising a retainer that is disposed to contact an upstream side of the heater section, wherein the heater section is in contact with the catalyst section, the retainer has an insulating property and allows passage of the exhaust gas therethrough, and the heater section is sandwiched between the retainer and the catalyst section.
 5. The catalyst apparatus for the internal combustion engine according to claim 1, wherein the catalyst section includes at least a reduction catalyst.
 6. The catalyst apparatus for the internal combustion engine according to claim 2, wherein the heater section and the catalyst section are adjacently disposed in a common casing.
 7. The catalyst apparatus for the internal combustion engine according to claim 2, further comprising a retainer that is disposed to contact an upstream side of the heater section, wherein the heater section is in contact with the catalyst section, the retainer has an insulating property and allows passage of the exhaust gas therethrough, and the heater section is sandwiched between the retainer and the catalyst section.
 8. The catalyst apparatus for the internal combustion engine according to claim 3, further comprising a retainer that is disposed to contact an upstream side of the heater section, wherein the heater section is in contact with the catalyst section, the retainer has an insulating property and allows passage of the exhaust gas therethrough, and the heater section is sandwiched between the retainer and the catalyst section.
 9. The catalyst apparatus for the internal combustion engine according to claim 2, wherein the catalyst section includes at least a reduction catalyst.
 10. The catalyst apparatus for the internal combustion engine according to claim 3, wherein the catalyst section includes at least a reduction catalyst.
 11. The catalyst apparatus for the internal combustion engine according to claim 4, wherein the catalyst section includes at least a reduction catalyst. 